This application is a 35 USC 371 application of PCT/DE 00/02550 filed on Aug. 2, 2000.
1. Field of the Invention
The invention is based on a fuel injection system for an internal combustion engine and particularly to such a fuel injection system having at least two high system pressures.
2. Description of the Prior Art
One fuel injection system of the type with which this invention is concerned has been disclosed by European Patent Disclosure EP 0 711 914 A1.
For better comprehension of the ensuing description, several terms will first be explained in further detail: In a pressure-controlled fuel injection system, a valve body (such as a nozzle needle) is opened counter to the action of a closing force by the fuel pressure prevailing in the nozzle chamber of an injector, and the injection opening is thus uncovered for an injection of the fuel. The pressure at which fuel emerges from the nozzle chamber into the cylinder is called the injection pressure, while system pressure is understood to mean the pressure at which fuel is available or is stored in the injection system. The term stroke-controlled fuel injection system is understood in the context of the invention to mean that the opening and closure of the injection opening of an injector are done with the aid of a displaceable valve member, on the basis of the hydraulic cooperation of the fuel pressures in a nozzle chamber and in a control chamber. In a combined fuel metering, a switch is made between various injection pressures, and only one common valve is used for metering the fuel; the switchover can be done either centrally, that is, prior to the fuel distribution to the individual cylinders, or locally, that is, individually for each cylinder.
In the pressure-controlled injection system known from EP 0 711 914 A1, fuel is compressed to a first, high system pressure of about 1200 bar with the aid of a high-pressure pump and is stored in a first pressure reservoir. The fuel at high pressure is also pumped into a second pressure reservoir, in which by regulation of its fuel delivery by means of a 2/2-way valve, a second, high system pressure of about 400 bar is maintained. Via a valve control unit, either the lower or the higher system pressure is directed into the nozzle chamber of an injector. There, by means of the pressure, a spring-loaded valve body is lifted from its valve seat, so that fuel can emerge from the nozzle opening.
In this known injection system, it is disadvantageous that all the fuel must first be compressed to the higher system pressure level so that then some of the fuel can be relieved again to the lower system pressure level.
The fuel injection system of the invention, which can be pressure-controlled or stroke-controlled, in order to increase its efficiency, it is proposed that only the fuel for one pressure reservoir be compressed to the higher system pressure level, while the fuel for the other pressure reservoir is compressed only to the lower system pressure level.
What according to the invention is the lesser fuel quantity at the higher system pressure leads not only to higher efficiency but also to a reduced load on the pump components, and since the higher system pressure need not be sealed off from normal pressure but only from the other high, yet lower, system pressure, this leads to improved sealing and thus less leakage.